Wood panel overlay and method and manufacture



United States Patent 0 3,448,001 WOOD PANEL OVERLAY AND METHOD AND MANUFACTURE Reino A. Jarvi, Bellevue, Wash., assignor to Simpson Timber Company, Seattle, Wash., a corporation of Washington No Drawing. Filed May 31, 1966, Ser. No. 553,664 Int. Cl. B32b 21/08, 21/06 U.S. Cl. 161-261 19 Claims ABSTRACT OF THE DISCLOSURE High density paper overlaid plywood panels are produced by hot press bonding of resin impregnated paper onto the wood substrate without caul sticking. Caul sticking during hot press bonding is eliminated by employing a paper impregnated with a condensation polymer formed from the co-reaction of the phenol with an aliphatic chain para-substituted phenol and formaldehyde in the presence of an alkali hydroxide catalyst.

This invention relates to wood products overlaid with a resin impregnated paper for use as concrete forms or exterior surfacing. More particularly, this invention relates to such a composite material wherein a phenolic resin impregnated paper overlay has a high internal bond strength and is classified as a high density overlay.

High density overlay panels are particularly desirable for use as concrete forms because they can be reused over and over. These panels are particularly suited to such repeated use because of their ability to withstand severe caustic conditions caused by the curing concrete contacting the impregnated paper overlay; and their high resistance to pinking on white concrete, water absorption, checking and abrasion.

High density overlay panels are formed by impregnating paper sheet material with sufficient amounts of phenolic resin so that the impregnated paper can be hot press bonded directly to a wood substrate without the use of an intervening glue line. The wood susbtrate is usually exterior grade plywood but could be some other material, such as particle board. The face to which the impregnated paper overlay is bonded must be solid. A solid face may be obtained by use, as required, of wood patches, shims, or chemical patches.

Hot press bonding is accomplished by stacking an overlaid panel between the platens of a large press and then pressing the stack under high temperature conditions to set the resin. The panel substrates must have resin impregnated paper sheet material applied to both faces to prevent panel warping due to shrinkage as the phenolic resin is cured.

Caul sheets are placed between the top and bottom surfaces of the panels and the respective press platens to keep the platen surfaces free of resin. This use of caul sheets, which is essential, presents a severe manufacturing problem in that the phenolic resin impregnant sticks to the caul sheets during the 'hot pressing. This problem can be severe enough to close the hot presses in an assembly plant down completely.

One attempted solution has been to add chemical lubricating or release agents to the resin solution which is impregnated into the paper. Commonly used release agents have been the metal salts of saturated or unsaturated fatty acids. These release agents, if used in large enough quantities, are suificiently lubricative that the caul sheets tend not to stick to the hot pressed panels. This is not especially satisfactory, however, because the addition of a sufficient amount of a release agent reduces the alkali resistance of the finished overlay panel to an unacceptably low level. If ones hot presses are inactive because of caul sticking problems, however, the use of undesirably large amounts of a release agent are unavoidable.

Another attempted solution has been to use smaller amounts of a release agent and wax the caul sheets so as to present a nonsticking surface to the panel overlays. This is not particularly desirable because the 'wax leaves a residue on the hot pressed panel overlays which could detract from their usefulness as concrete form panels. Furthermore, such a residue prevents the overlaid panels from being used as exterior building materials which are to be painted, whereas the panels would otherwise be well suited to such use.

A primary object of this invention is to provide a proper overlaid panel without incurring the problems enumerated above. A further object is to provide such a paper overlaid panel which has a high resistance to alkali, pinking, water absorption, checking and abrasion. Another object is to provide a method of assembling such a paper overlaid panel that does not result in caul sticking or overlay surface contamination problems. These and other objects and advantages will become apparent from the following description.

In brief, the invention comprises a method of assembling a paper impregnated overlaid wood panel, and the resultant product, whereby a phenolic resin saturated paper sheet material is overlaid and hot press bonded to the faces of a wood substrate, the phenolic resin impregnating solution comprising (1) a condensation polymer formed from the co-reaction of phenol with an aliphatic chain para-substituted phenol and formaldehyde in the presence of an alkali hydroxide catalyst, and (.2) an external lubricating or release agent such as a metal salt of a long chain saturated or unsaturated fatty acid. It has been unexpectedly discovered that the para-substitutedaliphatic chain provides internal lubrication against metal for the phenol-formaldehyde polymer when a part thereof and also affords good alkali resistance. Consequently, only a small amount of an external lubricating agent need be added to eliminate caul sticking problems, which amount is below the amount that would deleteriously affect the alkali resistance of the hot pressed overlaid panel.

More specifically, it has been discovered that analiphatic chain para-substituted phenol having up to 17 carbon atoms provides the requisite degree of internal lubrication when employed in an equivalent of between 1 and 51() mol percent based on the total mols of phenol in the resin. Use in amounts below about 1 mol percent provides insuflicient internal lubrication to be effective. When the overlaid panel is to be used as concrete form material, use in amounts above about 5 mol percent results in a sharp drop in alkali resistance of the overlaid panel. When the overlaid panel is to be used as exterior building material and is to be painted, use in amounts above about 10 mol percent results in a resin cure that is impractically long with no offsetting increase in internal lubrication, the sharp drop in alkali resistance above 5 mol percent having no effect on panel utility where the panel overlay is to be painted. Para nonyl phenol, having an aliphatic chain with 9 carbon atoms, has been found to be particularly suitable for this invention. Para nonyl phenol appears to assist the cure of the reaction in providing a superior product.

Longer chain substituted phenols, such as para dodecyl phenol having an aliphatic chain of 11 carbon atoms, are less desirable because the resin is less soluble and its penetration is hampered. Thus, insuflicient resin pickup in the overlay may result With a concomitant decrease in alkali resistance and an increase in water transmission. Shorter chain substituted phenols, such as tertiary butyl phenol and tertiary pentyl phenol having aliphatic chains of 4 and 5 carbon atoms, respectively, are also less desirable alkali resistance decreases. These longer and shorter chain substituted phenols, however, also exhibit excellent caul release characteristics.

Metal salts of long chain saturated or unsaturated fatty acids having -21 carbon atoms are preferred external lubricants for the invention. A longer chain fatty acid metal salt does not dissolve satisfactorily and has an undesirable waxy character that deleteriously affects the paper overlay impregnated with the resin. A shorter chain fatty acid metal salt does not posses suflicient lubricating properties to be of any value. Fatty acids, although acceptable, are not preferred over saturated fatty acids because the latter have less effect on lowering alkali resistance of the overlaid panel. The dibasic metal salts of stearic acid, a saturated fatty acid, such as zinc or calcium stearate are preferred. Such dibasic metal salts are used in an amount equivalent to 1-1.6 wt. percent based on the total solids weight of the resin impregnating solution; amounts less than about 1 wt. percent being insufficient to eliminate caul sticking, and amounts greater than about 1.6 wt. percent producing no further lubricating effect.

The phenolic resin condensation polymer employed in the impregnating resin solution should have a solids content between about 65-75% so that the final solids content of the impregnating solution Will be within the range of about 48-55%. The formaldehyde is preferably provided as 37% uninhibited formalin in an amount sufficient to provide 2-2.6 mols of formaldehyde per mol ofthe total phenols, an optimum mol ration being about 2.3:1. A rnol ratio less than about 2:1 decreases the water solubility to the point where there will be insufiicient resin penetration into the saturating paper. A mol ratio greater than about 2.6:1 will increase the water solubility and resin penetration into the paper to the point where checking of the overlay becomes a serious problem. Methanol is added with the uninhibited formalin to bring its methanol content to about 2 /2 The preferred alkali catalyst is Na CO because its conversion to NaOH is sufficiently slow to keep the alkalinity of the resin relatively low and to control the reaction better by increasing the alkalinity slowly as the resin is prepared. The purpose of low alkalinity is to control the water solubility of resin for purposes of impregnation. NaOH itself would be acceptable but its use does not provide the desirable features inherent in the use of Na CO in the first instance. The resin would be suitably neutralized to a pH of about 6.8 as by addition of lactic acid.

The solids range of about 48-55% for the impregnating solution is necessary to enable impregnating the paper sheet material to a resin solids content of between about 18-55%. H the resin content of the paper is below about 48%, there will be insufiicient flow to bond the impregnated paper directly to the wood substrate. If the resin content of the paper is above about 55% the result ing impregnated paper will be too brittle and the overlaid panel will be unacceptably prone to extreme checking.

Any of the saturating paper known to those skilled in the art of impregnated paper overlaid panels are satisfactory in this invention. Bleached saturating paper having a weight of about lbs./ 1,000 sq. ft. on a bone dry basis produces a very acceptable impregnated overlay. Kraft saturating paper having a weight of about 50 lbs./ 1,000 sq. ft. on a bone dry basis is also acceptable and produces a tougher, more resistant overlay, although its esthetic appearance when impregnated may not be considered as pleasing as the appearance of the impregnated bleached saturating paper.

Melamine or hexamethylene tetramine is preferably added to the impregnating solution to catalyze the solution and accelerate its cure in the overlay. Melamine is preferred in an optimum amount of about 3 wt. percent based on the total solids weight of the resin impregnated solution. Use of more melamine would increase the alkali resistance of the overlaid panel but would also increase the tendency of the overlaid panel to check. Hexamethylene tetramine is not as desirable as melamine where the overlaid panel is to be used as concrete form material because its addition does not beneficially effect alkali resistance as much as the addition of melamine. However, the addition of hexamethylene tetramine does reduce checking problems more than does the addition of melamine.

An exemplary impregnating solution comprising 3.92 mol percent para nonyl phenol present in the phenolic resin is as follows:

TABLE I Parts by weight Phenolic resin at 66% solids 1,500 Water 194 Isopropyl alcohol 126 Melamine resin powder Water 100 Zinc Stearate (1.3 wt. percent based on resin solids) 14 Final resin solids 54% Flow 10%. Volatiles 8%.

The isopropyl alcohol is employed to initially dissolve the zinc stearate. The water-alcohol ratio can be varied to control the degree of resin penetration into the saturating paper. The exact ratio will depend on the type of saturating paper to be impregnated. In general, a higher waterzalcohol ratio will result in greater penetration but will also increase the checking tendency.

Saturating paper sheet material is drawn through a body of the resin impregnating solution such that a sufficient amount of resin solids has impregnated the paper.

It is believed that the invention will have been clearly understood from the foregoing detailed description of my now-preferred illustrated embodiment. Changes in the details of construction may be resorted to without departing from the spirit of the invention and it is accordingly my intention that no limitations be implied and that the hereto annexed claims be given the broadest interpretation to which the employed language fairly admits.

What is claimed is:

1. An article of manufacture which comprises a wood substrate; and a phenolic resin impregnated paper overlay bonded to at least one face of said wood substrate, the phenolic resin impregnant comprising a condensation polymer formed from the co-reaction of phenol with an aliphatic chain para-substituted phenol and formaldehyde using an alkali hydroxide catalyst.

2. An article according to claim 1 wherein said aliphatic chain para-substituted phenol comprises para-nonyl phenol.

3. An article according to claim 1 wherein said allphatic chain para-substituted phenol comprises 1-10 mol percent based on the total mols of phenol.

4. An article according to claim 1 wherein said aliphatic chain para-substituted phenol comprises 1-5 mol percent based on the total mols of phenol.

5. An article according to claim 1 including a lubricant selected from the group consisting of metal salts of long chain saturated or unsaturated fatty acids having 15-21 carbon atoms.

6. An article according to claim 1 including a lubricant selected from the group consisting of zinc stearate and calcium stearate.

7. An article according to claim 1 wherein said paper overlay comprises paper sheet material selected from the group consisting of bleached saturating paper and kraft saturating paper.

8. A resin impregnating solution comprising a resin formulated from the co-reaction of phenol with an aliphatic chain para-substituted phenol and formaldehyde in the presence of an alkali hydroxide catalyst, and a dibasic metal salt of stearic acid.

9. A resin impregnating solution according to claim 8 wherein said aliphatic chain para-substituted phenol comprises 1-10 mol percent based on the total mols of phenol.

10. A resin impregnating solution according to claim 8 wherein said aliphatic chain para-substituted phenol comprises 1-5 mol percent based on the total mols of phenol.

11. A resin impregnating solution according to claim 8 wherein said aliphatic chain para-substituted phenol comprises para-nonyl phenol.

12. A resin impregnating solution according to claim 8 including a lubricant selected from the group consisting of zinc stearate and calcium stearate, said lubricant being provided in an amount equivalent to about 1-1.6 wt. percent of resin solids in said solution.

13. A resin impregnating solution according to claim 8 wherein the resins solids of said solution is between about 48-55%.

14. A resin impregnating solution according to claim 8 wherein said resin is formulated by co-reaction of 2-2.6 mols of formaldehyde per mol of total phenols in the presence of Na CO catalyst.

15. A method of fabricating on overlaid building material comprising providing a wood substrate; providing a resin impregnating solution comprising a resin formulated from the co-reaction of phenol with an aliphatic chain para-substituted phenol and formaldehyde in the presence of an alkali hydroxide catalyst, and a di'basic metal salt of stearic acid; impregnating a paper sheet material with the resin solution; and hot press bonding the impregnated paper sheet material to said wood substrate.

16. A method according to claim 15 wherein said resin is formulated by co-reaction of 2-2.6 mols of formaldehyde per mol of total phenols in the presence of Na CO catalyst.

17. A method according to claim 15 wherein said aliphatic chain para-substituted phenol comprises paranonyl phenol.

18. A method according to claim 15 wherein dibasic metal salt of stearic acid is selected from the group consisting of zinc stearate and calcium stearate in an amount equivalent to about 1-1.6 wt. percent resin solids in said solution.

19. A method according to claim 15 wherein the resin solids of said resin impregnating solution is between about 4855% DONALD E. CZAJA, Primary Examiner.

WILLIAM E. PARKER, Assistant Examiner.

U.S. Cl. X.R. l61--268; 260-19, 53 

